It is now a world tide and wave that worldwide material recycling is being increasingly important in the field of waste disposal. Additionally, refuse is a large source of heat energy. High energy recycling processes may be used to increase investment profits from refuse incinerators and further prevents environmental pollution caused by the incinerators during operation.
In a conventional incinerator, the refuse is directly thrown into the incinerator for combustion with a mixture of air flowing under a furnace grate. However in such systems, the refuse is generally wet and combusts slowly due to the fact that it requires a lengthy period of time before the refuse dries and begins to burn. In addition, the combustion gas produced in such burning processes, owing to a required higher incinerator temperature, provides a gas density less than that of the entrance air. In such systems the combustion gas does pass down to the grate once it has risen. Therefore, the oxygen remaining in the combustion gas rarely comes in contact with the refuse again for assisting in the burning process. Thus, the excess air ratio required in the burning process cannot be reduced during operation and the temperature of the combustion gas cannot be increased to any great extent.
The value of the excess air ratio for the burning of various fuels is influenced by the refuse moisture content and ignition temperature and also depends on the total contact surface between fuel and air while burning.
Generally, if the fuel used is highly combustible and has a low moisture content, then a lower amount of excess air ratio is required in the burning process. Additionally, with high contact surface areas between the fuel and air a lower amount of excess air ratio is required. Opposingly, if the fuel has a greater moisture content or there is less contact surface area between fuel and air during combustion then a larger excess air ratio is required.
As an example, with respect to the burning of natural gas, such has little moisture content, is easy to ignite and mixes completely with air during burning, leading to an excess air ratio of only about 1.08. In the burning of coal, although it has a low moisture content and is easy to ignite, due to its compact form the total contact area between the coal and air is less than that of natural gas, and thus the excess air ratio is found to be increased to 1.25. As another example as to the burning of bagasse in a prior art bagasse furnace, although the bagasse is combustible, and its incompact form will greatly increase the total contact surface between the bagasse and air, due to its 45% moisture content, the required excess air ratio is about 1.5. Lately, in the modern bagasse furnaces which are equipped with the spreader stokers, the bagasse shreds are dried while they are spread into the furnace and fall through the combustion gas to burn on the grate. In this case, the excess air ratio has been found to be reduced closer to 1.25.
It has been found that in the incineration of the Taipei municipal combine refuse, in spite of its incompact form the ignition temperature of the combustibles are much like the bagasse, and because of its large percentage of moisture content (about 56%), the excess air ratio requirement increases to 2.0. In the same way, while the wet refuse has been completely dried it is burnt immediately on the grate much in the manner of the bagasse. In this case the excess air ratio is reduced and approaches 1.3, while the combustion temperature is raised.
The higher the combustion temperature, the higher the percentage of energy transformation from steam into mechanical energy and electric energy in an electric generating system operated by steam power. Electrical generation by coal, oil or natural gas is performed by combusting gas temperatures as high as 1540.degree. C. (2800.degree. F). The percentage of transformation from heat energy into electric energy being approximately 40%. But refuse burned in known combusting equipment only produce burned gas having a temperature as low as 850.degree. C., with a transformation percentage being only 20%. Electric energy transformation percentages from the different temperatures of combustion gas via the steam-power cycle may be estimated by an interpolation method.